1. Field of the Invention
The invention relates to a microwave transmitting device for a level measuring device with an electronic device, a microwave emitter and a waveguide, wherein the inside of the waveguide is cast with casting compound. The invention relates further to a level measuring device having such a microwave transmitting device.
2. Description of Related Art
Level measuring devices are normally used to monitor the level of liquids or bulk solids in containers. The methods for measurement used in this case are diverse and include, for example, mechanical measurement methods, such as float gauges or vibration sensors, but also capacitive, conductive and optical measurement methods. The methods used for measurement are differentiated into contact and non-contact measurement methods. Radar technology in the microwave range and neighboring frequency ranges are used particularly often in non-contact measurement methods. The invention is based on such a level measuring device and a microwave transmitting device used therein.
Of course, not only can the fill level of a medium in a container be determined with a level measuring device using the radar principle and a corresponding microwave transmitting device, but rather arbitrary distances from surfaces to the “level measuring device” or to the microwave transmitting device, which reflect microwaves emitted from the measuring device or from the transmitting device; nevertheless, a level measuring device or a microwave transmitting device for such a level measuring device are the topics of discussion.
A level measuring device of this type has a microwave transmitting device, wherein the microwave transmitting device includes an electronic device for generating microwave signals, a waveguide for guiding the microwave signals and a microwave emitter, wherein the microwave emitter couples the microwave signals into the waveguide. These microwave signals are guided by the waveguide and are emitted in the container in which the medium whose level is to be determined is found. These microwave signals are reflected by the medium in the container and return in the waveguide to the microwave emitter, which usually acts simultaneously as microwave receiver.
A device for determining the fill level of contents in a container is known from International Patent Application Publication WO 02/16889 A1 having a signal-generating unit that generates electromagnetic measuring signals, having a sending/receiving unit that emits the measuring signal via an antenna in the direction of the surface of the contents and receives the echo signals reflected on the surface of the contents, wherein the antenna consists of a waveguide that expands in the direction of radiation in a cavity of a defined form and having an evaluation unit that determines the fill level in the container using the running time of the measuring signal. This level measuring device reduces deposits, i.e., that the deposit of a medium on the device is nearly eliminated in that a dielectric filling material is provided that at least partially fills the waveguide and nearly completely fills the expanded cavity of the antenna.
U.S. Pat. No. 6,987,481 B2 discloses a radar level measuring device that is capable of generating and receiving an elliptical polarized wave with a directional coupler. The radar level measuring device further has a waveguide closed on one side, which is cast with a casting compound.
Level measuring devices known from the prior art have a disadvantageous size, in particular when there is a shortage of space at the mounting site of the measuring device, access to the mounting site is confined or the cavity to be measured has smaller dimensions. This size is limited downward to a minimum in that, at a given frequency of the used microwave radiation, the stripline and/or waveguide components normally used for guiding and integrating the used microwave radiation must have a minimum size, so that the stripline or waveguide components are capable even of guiding the microwave radiation at low loss.